1. Technical Field
The present invention relates to a progressive-power lens.
2. Related Art
A progressive-power lens includes a distance portion having the power (dioptric power) corresponding to distance vision, a near portion having the power corresponding to near vision, a progressive portion provided between the distance portion and the near portion, and an intermediate lateral portion provided on both sides of the progressive portion. A difference between the power of the distance portion and the power of the near portion is referred to as an addition power (Add), and, as the addition power becomes larger, discomfort such as fluctuation, distortion, and blurring is increased. In addition, when the progressive-power lens is fitted, adjustment is typically performed such that optical performance in the distance portion becomes the best, and thus a position of the near portion is necessarily set. Therefore, optimal fitting in the near portion may not be performed independently. When such a progressive-power lens is actually worn, the eye-perceived near dioptric power is different from the lens dioptric power, and thus fluctuation or distortion is worsened.
There have been proposed techniques for suppressing such discomfort (for example, refer to Japanese Patent No. 3582527). A progressive-power lens disclosed in Japanese Patent No. 3582527 includes an object-side surface and an eye-ball side surface, wherein when an average curvature of the eyeball-side surface around the distance portion is used as a reference spherical surface, an average curvature of the eyeball-side surface around the near portion is changed such that the eyeball-side surface around the near portion is located closer to an eyeball side than the reference spherical surface.
When the progressive-power lens disclosed in Japanese Patent No. 3582527 is actually worn, the problems such as image distortion or fluctuation can be reduced to some degree, but it is not sufficiently satisfactory, and further reduction is necessary.
Particularly, in a progressive-power lens of the negative dioptric power, there is a problem in that there is an occurrence of distortion where an image looks long in the vertical direction in the regions from the progressive portion to the near portion.